There are many instances in which an individual working in an atmosphere hostile to breathing is provided with a mask assembly which covers the nose and the mouth. In many instances the mask assembly is provided with a communication system including an external lead having a plug adapted to be inserted into an intercom or radio system. One particular system of this type known in the art is a helmet assembly provided with sound attenuating earcups which exclude ambient sound but which are provided with earphones adapted to receive signals from a radio, or intercom system, or the like. Many of these helmet assemblies are provided with oxygen masks which cover the nose and the mouth of the wearer and which are supplied from a suitable source of oxygen to permit the wearer to function in a rarified atmosphere or in an atmosphere which is contaminated. In such combined helmet and mask assemblies, either the helmet assembly may be provided with a contact microphone or the mask assembly may be provided with a microphone. In either instance, the microphone likewise is adapted to be plugged into a radio or intercom, or combined radio and intercom system. One specific example of such a combined mask and helmet assembly is that used by the crews of high performance aircraft. In such instances, when the crew man is in position in the aircraft, his oxygen hose is releasably connected to the oxygen supply and his communication system is plugged into the radio and inter system. When he leaves the aircraft, the hose is detached from the supply and his communication system is unplugged.
When the crew man of an aircraft of the type described above is in the "ready" room, he is required to be so equipped as to be able to take his position in the aircraft in the shortest possible period of time. In order to be in such condition, he should have his helmet on and he may even have his mask in position over his nose and mouth and in sealing engagement with his face, so that he breathes through the disconnected oxygen hose or through a filtered air source.
Under the condition just described, the wearer of the helmet and mask assembly cannot communicate locally. First, the sound attenuating earcups of the helmet assembly prevent him from hearing ambient sounds. Secondly, he cannot be heard to speak since his nose and mouth are sealed from the outside atmosphere, except through the disconnected oxygen supply tube or filter assembly, so that any attempt on his part to speak would be muffled.
Similarly any other individual wearing a mask having a communication arrangement adapted to be plugged into an external system cannot communicate locally while wearing the mask.